[platimus]

I could actually see 80-90% of the Talents as being self-taught or learned through the course of adventuring and practicing on one's own.

Spells are an entirely different story.

EDIT
I agree with Skarg's post just above mine. He posted while I was writing this one. This post was more of a response to Shadekeep's and Hcobb's posts. I mostly disagree with Shadekeep's.